Oil sand slurry transportation system and method for variable slurry flow rates

ABSTRACT

Provided is a system for transporting an oil sand slurry, comprising a pump, upstream and downstream lines, a shaft connectable to the pump, a driving mechanism driving the pump and a regulator for regulating the torque applied to the shaft between positive and negative torque modes, to pump the slurry at higher or lower flow rates. Also provided is a method comprising pumping the slurry through a pipeline using a pump driven by a motorised shaft and adjusting the flow rate of the slurry by varying the torque applied to the motorised shaft between positive and negative torque modes. The oil sand slurry transportation system and method enable positive head (regular pump action) for normal and high flow rates and negative head (pump brake action) for low flow rates, which reduces system energy loss, pipeline wear, vapour breakout and sanding off.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. Ser. No.12/960,096 filed Dec. 3, 2010, the subject matter of which isincorporated herein by reference in entirety.

FIELD OF THE INVENTION

The invention generally relates to the field of transporting oil sandslurries, and more particularly to a system and method of transportingan oil sand slurry.

BACKGROUND

In traditional mining, slurry pipeline systems are built withsignificant reservoir capacity to maintain a steady flow rate. Oil sandsslurry pipeline systems have limited reservoir capacity and as a resultmay have a highly variable flow rate. The flow rate may be increased ordecreased for a variety of reasons depending on, for instance, changingupstream availability of oil sands slurry as well as other processoperating constraints.

Enabling efficient flow of a slurry, such as oil sands slurry, through apipeline also requires some operating conditions that are not normallyrequired for other liquids. For instance, it is desirable to maintain anadequate flow rate in the pipeline when operating at low flow rates toavoid “sanding off”, which is when some of the oil sands normallysuspended in the solvent come out of suspension thereby hindering theflow and increasing wear on pipeline equipment.

Variable flow rate slurry flowing downhill in undulating terrain, suchas in an oil sands mine, thus requires a smaller pipeline diameter inorder to maintain adequate line pressure during times of reduced flowrate. Unfortunately, using a smaller pipeline diameter results inexcessive pipeline wear and system energy loss at normal or high flowrates. Current industry practice is to accept the energy loss andinstall sacrificial wear components such as reduced line size sections,orifice plates or valves.

Oil sands mining and transportation are also fraught with harshconditions and oils sands slurry can be more damaging on pipelineequipment than other fluids and suspensions traditionally transported bypipeline.

There is currently a need for a technology that overcomes at least oneof the disadvantages of what is currently known and used in the field.

SUMMARY OF THE INVENTION

The present invention responds to the above-mentioned need by providinga slurry transportation system and method for transporting slurry.

More particularly, the present invention provides a slurrytransportation system for transporting an oil sand slurry, comprising:

-   -   a pump having an inlet for receiving the slurry and a discharge        for discharging the slurry;    -   an upstream line in fluid communication with the inlet and a        downstream line in fluid communication with the discharge;    -   a shaft connectable to the pump;    -   a driving mechanism connectable to the shaft to drive the same        to operate the pump;    -   a regulator connectable to the driving mechanism for regulating        the torque applied to the shaft, to allow the driving mechanism        to drive the shaft in a positive torque mode to cause the pump        to discharge the slurry at a higher flow rate, or in a negative        torque mode to cause the pump to discharge the slurry at a lower        flow rate.

The present invention also provides a slurry transportation method fortransporting an oil sand slurry, comprising:

-   -   pumping the slurry through a pipeline using a pump driven by a        motorised shaft; and    -   adjusting the flow rate of the slurry by varying the torque        applied to the motorised shaft between a positive torque mode        enabling the pump to discharge the slurry at a higher flow rate,        and a negative torque mode enabling the pump to discharge the        slurry at a lower flow rate. to the motorized shaft if the        downstream flow rate is to be low.

The oil sand slurry transportation system and method enable positivehead (regular pump action) for normal and high flow rates and negativehead (pump brake action) for low flow rates. This pump brake action canreduce system energy loss and pipeline wear, for instance due toeliminating the requirement for a reduced size section and allowinglarger overall line size, while enabling efficient reduction of vapourbreakout and sanding off.

The positive-negative torque regulation allows efficient adaptation tovariable oil sands processing and transportation conditions. By allowinga negative torque to be applied to the shaft, the flow rate can bereduced in a simple and efficient manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic of one embodiment of the presentinvention.

FIG. 2 is a block diagram schematic of another embodiment of the presentinvention.

FIG. 3 is a block diagram schematic of yet another embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the oil sand slurry transportation system 10are illustrated in FIGS. 1-3.

The oil sand slurry transportation system 10 is preferably integratedinto a pipeline system for transporting slurry such as oil sands slurryto downstream reservoirs or processing units. The slurry may include avariety of oil sands slurries, such as at-face mined oil sand slurry,primary or secondary middlings or tailings slurries, fine tailings ormature fine tailings slurry. Depending on their origin and stage ofprocessing, the oil sand slurries contain various quantities of sand,bitumen, clay, chemical processing additives and other compoundsinherent to the mined oil sand ore.

The slurry transportation system 10 includes a pump 12, an upstream line14 and a downstream line 16, a shaft 18 connected to the pump 12, adriving mechanism 20, and a regulator 22.

It should be understood that the upstream and downstream “lines” arepreferably pipelines but may also be the inlet or outlet of processingequipment such as tanks, reaction vessels, and the like.

Referring to FIG. 1, the pump 12 may be a centrifugal pump having animpeller (not illustrated) connected to a shaft that is driven by thedriving mechanism 20 which in this case consists of a motor 24. Thedriving mechanism 18 is in turn coupled to the regulator 30 whichregulates the torque applied to the shaft, to allow the drivingmechanism 18 to drive the shaft 18 in a positive torque mode to causethe pump 12 to discharge the slurry at a higher flow rate, or in anegative torque mode to cause the pump to discharge the slurry at alower flow rate.

It should be understood that “negative torque mode” includes the pointat which zero torque is applied. At this point, there will only be apressure drop across the pump that amounts to the friction losses withinthe pump. It should also be understood that “higher flow rate” and“lower flow rate” are meant relative to each other.

The pump 12 has an inlet 26 for receiving the slurry from the upstreamline 14 and a discharge 28 for expelling the slurry through thedownstream line 16. It should be noted that the centrifugal pumps 12used in this system 10 can be further adapted to improve efficiency ofproviding negative head, for example with tailored impeller design.

Referring to FIG. 1, the driving mechanism 18 is a single motor 24 andthe regulator 30 includes a variable frequency device 32 (hereafterreferred to as a VFD). The VFD 32 is programmed to operate the motor 24in such a way that a positive torque is applied to the shaft 18 duringtimes of high process flow rates and a negative torque is applied to theshaft 18 during times of low process flow rates. The VFD 16 may bepowered by the power grid 34.

Still referring to FIG. 1, the regulator 22 may also include a controlunit 36 that is coupled to the VFD 16. The control unit 36 monitorsvarious operating conditions, makes calculations to determine thedirection and magnitude of torque to be applied, and provides signals tothe VFD 16 to change or otherwise regulate the torque applied to theshaft 18 to obtain given flow rates and slurry pressures.

The control unit 36 can calculate the torque to be applied based on anumber of variables. For instance, the pressure at the pump inlet, thepressure change in the pump, the slurry composition, the friction lossin the pipeline system, and other upstream and downstream constraints,may be used to calculate the applied torque to obtain a given slurryflow rate. There are a number of empirical equations and calculationmethods to determine the flow rate and corresponding torque to apply.

In operation, the slurry transportation system 10 can allow high, normalor low flow rates, which will be described below.

Normal and High Flow Rates—Positive Head

For a normal or high flow rate, a positive torque is applied to theshaft 18 so that there is a head gain between the pump inlet and thepump discharge. At these flow rates, it can be said that there isregular pump action.

Flow Rate Transition

In response to a requirement for a decreased slurry flow rate, thepositive torque applied to the shaft is reduced. At zero applied torque,there will only be a pressure drop across the pump that amounts to thefriction losses within the pump.

Low Flow Rates—Negative Head

When the flow rate is to be further decreased, for instance in responseto a requirement for greater back pressure, a negative torque is appliedto the shaft to resist the flow of fluid through the pump 12. At suchlow flow rates the control unit 36 determines the optimal negativetorque to be applied to the shaft 18, and communicates this to the motor24 via the VFD 32.

The negative torque may be set in order to allow the slurry to flow atsufficient rate and pressure so as to maintain the oil sands solids inflowable suspension and thus reduce or avoid “sanding off”. It is notedthat a pressure above the vapour pressure of the solvent does not impactsanding off. It is also noted in this regard that the turbulence of theslurry flow will be a function of the rate and line size.

The negative torque may also be set and transitioned to in order tominimize the likelihood of vapour breakout, which would occur at higherelevations relative to the pump where the pressure is low and may behundreds of meters from the pump. Applying negative torque reduces oreliminates vapour breakout, since it increases the pressure drop acrossthe pump thus increasing the pressure further upstream to increase theline pressure above the vapour pressure of the slurry solvent.Furthermore, the negative torque mode capability of the system allowscontrolled and continuous flow rate adjustment for transient conditionsexperienced in oil sands mining and pipeline transport.

The slurry transportation system 10 is particularly applicable indownhill undulating terrain such as in oil sands mining and slurrytransport, as illustrated in FIG. 3, since the system pressure in suchcases is sufficient to allow the slurry to flow via gravity to itsdestination without a pump at a flow rate that may be called the no-pumpflow rate. Thus, when an even lower flow rate is desired, the slurrytransportation system 10 causes a braking action in the pump 12 innegative torque mode. It should be understood that the inlet pressure issufficiently greater than the discharge pressure, as a result of thebraking action of the pump 12 in low flow rate conditions.

In the preferred embodiment of the slurry transportation system 10illustrated in FIG. 1, there is a single variable speed and directionmotor 24 coupled to the pump 12 and regulated by the VFD 32 for applyingpositive or negative torque to its shaft 18.

In another optional embodiment of the system 10 as illustrated in FIG.2, there can be a motor 24 and a generator 38 coupled to a single pump12. The coupling of the motor 24 and the generator 38 may be ondifferent sections of the shaft 18.

The motor 24 can apply a positive torque to the pump 12 and thegenerator 38 can apply a negative torque. The motor/generator embodimentcan be controlled by one or more regulator 22, which may include a VFD,to enable a positive or negative torque mode.

Referring to FIG. 1, in one optional aspect of the slurry transportationsystem 10, when operating in negative torque mode, the system 10dissipates the braking energy by either sending it back as reject energyto the power grid 34. Referring to FIG. 3, the braking energy may bedelivered to an energy receptor 40 electrical load resistor. A varietyof regenerative braking techniques may be employed to recover thebraking energy as electricity or as heat for reuse in the system or themining operation at large. Thus, in negative torque mode, the inletslurry pressure is divided into braking energy and the discharge fluidpressure. The discharge fluid pressure should of course be sufficient toallow the oil sands slurry to flow properly downstream. The control unit36 may monitor and control the torque magnitude and direction.

The slurry transportation method of the present invention fortransporting slurry, includes pumping the slurry through a pipelineusing a pump driven by a motorised shaft; and adjusting the flow rate ofthe slurry by varying the torque applied to the motorised shaft betweena positive torque mode enabling the pump to discharge the slurry at ahigher flow rate, and a negative torque mode enabling the pump todischarge the slurry at a lower flow rate. The illustrated embodimentsof the system 10 may be used to perform this method.

The embodiments of the slurry transportation system and method enable anumber of advantages. For instance, traditional methods of increasingback pressure with valves and orifice plates that suffer from excessivewear can be reduced or avoided. In addition, by using the system of thepresent invention, pipeline wear and system energy loss can be reducedduring times of normal and high process flow rates. At normal and highflow rates the pump operates in the standard way, the reduction ofenergy loss and component wear results from using larger pipes. In otherwords, the system exerts continuous and adaptive control over the flowrate of the slurry so that low flow rates can be achieved in largerpipes while respecting the pressure requirements for maintaining thedesirable flow properties of the oil sands slurry. Thus, larger pipelinediameters can be used to increase the maximum flow rate, reduce pipelinewear and reduce system energy loss.

In addition, existing pipeline systems may be retrofitted with theslurry transportation system 10 of the present invention. In such acase, the slurry transportation system 10 allows increased adaptabilityin achieving low flow rates by avoiding equipment such as throttlingvalves and orifice plates. The continuous control of the flow rateoptimizes energy use and minimizes pipeline wear in the transientconditions of oil sands mining.

In one preferred aspect of the slurry transportation system, the pump islocated in-line in a pipeline and the pipeline does not require anyadditional units for increasing or decreasing the slurry pressure. Forinstance, the slurry transportation system enables avoiding thenecessity of open-ended cylinders and the like integrated in thepipeline. The pipeline with in-line pump thus may be a closed-system.Alternatively, there may be additional units in combination with someembodiments of the present invention to further increase or reduce theline pressure, depending on elevation, flow rate requirements (forinstance, outside of preferred flow rate ranges), pump design and othervariables. Furthermore, there may be one or more additional pumps, eachwith its corresponding driving mechanism, shaft, and regulator, arrangedin series with the first. One regulator could also control the magnitudeand direction of both pumps. This in-series arrangement may be used insituations of high elevation change and of very high or low flow rates.It should also be noted that the system may include various in-series orin-parallel pump combinations tailored to a given pipeline topography.

It should be understood that numerous modifications could be made to theembodiments of the present invention described hereinabove, withoutdeparting from what has actually been invented. For instance, differentconfigurations of the system may employ one or more pumps, motors, shaftsections connected to parts of the driving mechanism, VFDs and controlunits, in various configurations, given the constraints of the oil sandsmine and desired operating conditions.

1. A method of recovering energy from a flow of an oil sand slurrycomprising water, bitumen and suspended solids including sand, themethod comprising: producing the flow of the oil sand slurry from an oilsand mining operation; applying a negative head to the flow of the oilsand slurry; and recovering a braking energy from an application of thenegative head.
 2. The method of claim 1, further comprising reusing thebraking energy as electricity in the oil sand mining operation.
 3. Themethod of claim 1, comprising reusing the braking energy as electricityand sending the electricity obtained from the braking energy to a powergrid.
 4. The method of claim 1, further comprising reusing the brakingenergy as heat in the oil sand mining operation.
 5. The method of claim1, wherein producing the flow of the oil sand slurry comprises conveyingthe oil sand slurry at least partially by gravity.
 6. The method ofclaim 1, wherein applying the negative head comprises conveying the oilsand slurry through an in-line generator.
 7. The method of claim 1,wherein applying the negative head comprises regulating the flow of theoil sand slurry with a variable frequency device.
 8. The method of claim1, wherein applying the negative head comprises applying a pump brakingaction.
 9. The method of claim 1, wherein recovering the braking energycomprises delivering the braking energy to an energy receptor.
 10. Themethod of claim 9, wherein the energy receptor comprises an electricalload resistor.
 11. The method of claim 1, further comprising monitoringa direction of the flow of the oil sand slurry.
 12. The method of claim1, further comprising controlling the application of the negative headto reduce or avoid upstream vapour breakout from the flow of the oilsand slurry.
 13. The method of claim 1, wherein the oil sand slurrycomprises at-face mined oil sand slurry.
 14. The method of claim 1,wherein the oil sand slurry comprises primary middlings slurry orsecondary middlings slurry.
 15. The method of claim 1, wherein the oilsand slurry comprises tailings slurry.
 16. The method of claim 1,wherein the application of the negative head is performed during timesof low process flow rates.
 17. A system for recovering energy from aflow of an oil sand slurry comprising water, bitumen and suspendedsolids including sand, the system comprising: an upstream line in fluidcommunication with an oil sand mining operation and a downstream line,the upstream and downstream lines being configured for conveying the oilsand slurry from the oil sand mining operation; a negative head assemblymountable to the upstream and downstream lines to apply a negative headto the flow of the oil sand slurry; and an energy receptor electricallyconnectable to the negative head assembly for recovering a brakingenergy from the negative head assembly upon an application of thenegative head.
 18. The system of claim 17, wherein the downstream lineextends to a lower elevation than the upstream line, allowing the oilsand slurry to be conveyed at least partially by gravity.
 19. The systemof claim 18, wherein the upstream and downstream lines are arranged in agenerally downhill and undulating configuration.
 20. The system of claim17, wherein the negative head assembly comprises a pump having an inletfor receiving the oil sand slurry and a discharge for discharging theoil sand slurry.
 21. The system of claim 20, wherein the upstream lineis in fluid communication with the inlet and the downstream line is influid communication with the discharge.
 22. The system of claim 20,wherein the pump is a centrifugal pump having an impeller for allowingpumping of the oil sand slurry.
 23. The system of claim 20, wherein thepump comprises a driving mechanism having a motor and a regulator forregulating a discharge flow rate.
 24. The system of claim 23, whereinthe regulator comprises a variable frequency device electricallyconnectable to the motor.
 25. The system of claim 24, wherein theregulator further comprises a control unit coupled to the variablefrequency device to automatically control the application of thenegative head.
 26. The system of claim 23, wherein the regulator isconfigured to regulate the direction and magnitude of the flow of theoil sand slurry to allow sufficient flow rate and pressure to maintainparticles in suspension within the upstream and downstream lines andreduce or avoid sanding off.
 27. The system of claim 23, wherein theregulator is configured to control the application of the negative headto reduce or avoid vapour breakout from the flow of the oil sand slurryin the upstream line.
 28. The system of claim 17, wherein the negativehead assembly comprises a generator for applying the negative head tothe flow of the oil sand slurry.
 29. The system of claim 17, wherein theenergy receptor comprises an electrical load resistor.
 30. The system ofclaim 29, wherein the braking energy is reused as electricity in the oilsand mining operation.
 31. The system of claim 29, wherein the brakingenergy is reused as electricity and the electricity obtained from thebraking energy is sent to a power grid.
 32. The system of claim 17,wherein the braking energy is reused as heat in the oil sand miningoperation.
 33. The system of claim 17, wherein the oil sand slurrycomprises at-face mined oil sand slurry.
 34. The system of claim 17,wherein the oil sand slurry comprises primary middlings slurry orsecondary middlings slurry.
 35. The system of any one of claim 17,wherein the oil sand slurry comprises tailings slurry.
 36. The system ofclaim 17, wherein the negative head assembly applies the negative headduring times of low process flow rates.